Abstract
Instability phenomena occurring in the microstructure of micro-structured composites are numerically investigated. To this aim, an interface constitutive law is proposed to describe both decohesion and contact at bi-material interfaces. These formulations are implemented in the FE code FEAP. Then, by applying dimensional analysis, the nondimensional parameters governing the macroscopic response of the composite are identified. According to this model, transverse debonding with respect to the fiber direction is simulated and the transition from snap-back instability in case of coarse fiber diameters, to a stable mechanical response for finer reinforcements is quantified. These results provide a possible quantitative explanation to the role played by the size of the reinforcement on the instability phenomena experimentally observed during superplastic deformation.